Art of spray drying soap



Oct 28', 19 30.

E. P. STEVENSQN ET AL ART OF SPRAY DRYING SOAP Filed Aug. 28, 1928 mum 2 Sheets-Sheet l 57 as I fivveazions': In? 1? SZevemon 2 .51. ofiar Oct. 28, 1930. STEVENSON El AL 1,779,516

ART OF SPRAY DRYING SOAP Filed Aug. 28, 1928 2 Sheets-Sheet 2 1721202210219: Earl 22 Sievemon '.Fo? er Patented Oct. 28, 1930 UNITED STATES PATENT OFFICE" EARL P. STEVENSON, O1 NEWTON, AND BEN B. FOGLEB, OF BELMONT, MASSAGHl T SETTS ASSIGNORS To ARTHUR n. LITTLE, mconronArnn, same, A. conromvrron or mssAcnUsETT s OF CAMBRIDGE, MASSAOHU:

ART OF SPRAY DRYING SOAP Application filed August as, 1928. Serial no. 802,634.

This invention relates to a process and apparatus for the spray drying of soap and to the resulting product. While it will be of more general applicability, the invention is particularly adapted and designed to the production of a soap product having certain desirable characteristics.

It is a characteristic of spray dried products generally, when made by atomizing or finely distributing the substance to' be dried into-a very hot drying medium, that they are composed mainly of hollow particles tending generally to the spherical shape. This is true of most spray dried products. whether made, for example, from waste sulfite liquors, milk, chocolate, blood serum,

or other substances as well as soap. As would be anticipated from the well-known extensibility and elasticity of soap films, ex-

emplified in blowing soap bubbles, it is necessary in spray drying soap solutions to take extraordinary precautions lest the soap particles be so far extended as to give a product of undesirable bulk. An important purpose of the present invention is to provide means for controlling this tendency of spray dried soap to over-bulk.

Another important feature of the invention is to provide for removing the soap particles from the action of the drying medium at any predetermined stage of drying, thus admitting of controlling the water content in the finished roduct, as well as the bulk of the product. ll hen, as is generally the case, the material being dried is carried through and out of the drying chamber in a current of heated air it has heretofore been necessary to carry the degree of drying to the point at which the product is not sticky, as otherwise it would accumulate in and upon and quickly foul the separator system, which has heretofore usually been either a set of air filters or a cyclone separator. Inasmuch as the efliuent airfrom the spray dryer is 45 substantially above ordinary atmospheric temperatures, it has been necessary to carry the drying to such a point that the material will not be tacky or sticky at the temperature of its removal from the drying system. This often produces a product dryer than desired.

In order to regulate the degree of drying of the soap and to retain in a spray dried soap the optimum of moisture content it should be removed from the drying medium at thedesired predetermined stage of drying, and

should subsequently be removed from the dryer system at a temperature substantially below that 'of the normally effluent drying air. Conceivably this might be done by introducing into the drying chamber at some point a current of cooling air. Such method would be feasible providing intimate mixing of the cool and hot air currentscoul be obtained,

but in any event it is open to the'practical objection that it involves the handling of larger volumes of air in the separators, thus adding materially to the equipment and operating costs. With the new procedure of the formly sized product. The particularspraymg mechanism used in our apparatus, although constituting no part of the present invention, is very efiective in initially insuring against any substantial amount of objectionably fine particles. Yet it is impossible to secure perfect performance in this respect. An expedient commonly resorted to in spraying liquid soaps is to increase the size of small particles as initially formedv by excessive pufling, thus greatly increasing the bulk which the present invention is designed to prevent. The very small particles when introduced-into a current of very hot drying gas naturallybecome heated in the shortest time to a temperature above that at which Water boils, and at which an internal expansive pressure is created within the particle, with the result that such small particles are increased to asize out of all proportion to their mass. As such small, very light and over-bulked articles are objectionable in the finished pro not, it is desirable that they be eliminated, and preferably this should be done within the apparatus itself. In the resent invention such separation of the obectionably light and over-bulked particles is affected at that point in the process where the particles suitable for the final product are transferred from the drying current to the cooling medium.

Another feature of the invention is that it makes practicable the use of centrifugal spray mechanism in a horizontal chamber, which possesses certain operating advantages over a vertical chamber. A disadvantage of .a horizontal spray chamber, however, is that larger volumes of air than those required for the drying operation have heretofore ordinarily been required to prevent the particles from sticking on the sides of the chamber, particularly the bottom. The use of a tan gential air current producing as it does a swirl within the chamber is helpful to this end, but not sufficient in itself. The solution of the difliculty, according to the present invention, resides in the use of the combination of a horizontal spray chamber of particular form and an abutting Vertical tower, which together constitute an important feature of the invention, both as apparatus and as preferred means for performing the process. By spraying horizontally into a horizontal current of heated drying and conveying air in a horizontal chamber, and delivering the conveying current thence into a large vertical chamber or tower, into the lower part of which the particles that are to form the finished product fall by gravity out of the current of heated conveying air at the region where said current penetrates the tower, the current of heated air need be maintained at conveying velocity and conveying volume only a comparatively short distance, thus effecting material economies. A horizontal current of sufficient conveying velocity to carry the particles through and out of a horizontal drying apparatus would entail the use of heated air in a volume far out of proportion to the economic demands of the drying process; but by separating the particles from the horizontal conveying current after a fairly short travel, and permitting them then to fall by gravity for the remainder of their travel through the lower part of the tower, a much less volume of heated drying and conveying air is required. 7 The process of the present invention is capable of handling fluid soaps of widely varymg composition to yield in the hands of a skillful operator a uniform product which is not overbulked. Whereas other spray dryin methods, so far as we are aware, in which a uid soap is atomized into a current of hot drying air result in an unduly bulky product, weighing as little as 7.5 pounds to the cubic foot, it is well within the practical operating range of our process to secure a product weighing 20 pounds or even more to the cubic foot, that is, possessing less than onethird the bulk produced by such other methods. A practical result thereby achieved is that a product possessing all the intrinsic merits of a spray dried soap, may be manu factured without having, as an incident thereto, the increased distribution cost of an exceptionally bulky material.

Furthermore it is not necessary to reduce the moisture content of the product below 15% in order to make possible its separation from the spray drying system according to our invention. By our process, using the recommended apparatus, and the other recommended particulars, products containing as much as 20% of Water have been successfully manufactured.

Referring to the accompanying drawings, which illustrate our new form of apparatus, adapted to perform the process and produce the product in accordance with our invention,

Fig. 1 is a diagrammatic representation of the apparatus as a whole;

Fig. 2 is a cross section on line 2-2 of Fig. 1;

Fig. 3 is a longitudinal section on an enlarged scale of the preferred spraying or atomizing device; and

Fig. 4 is a diagrammatic representation of a modification of the spray chamber and associated parts of the apparatus shown in Fig.1.

The apparatus as a whole may be divided generally into the following elements or departments, namely, a soap reservoir and circulating system for conducting the fluid soa to the atomizing head; the atomizing head including a rotating cup into which the fluid soap is fed through a hollow'shaft; an air system for supplying heated air at both high and low pressure for atomizing and drying purposes; a horizontal spray chamber in which the initial drying takes place; and a Vertical tower for separating the partially dried soap particles from the current of heated drying gas and completing the drying to the desired point, and for cooling the par ticles in a zone of relatively cooler air which may, if desired, be an upward current of cool ing air, and/or conditioned air.

lVhen a fluid particle of soap is thrown from the rim of the rotating cup it immediately contacts with a current of heated drying and conveying air, which may be as much as 300 F. hotter than its own temperature. Under this drying potential the evaporation of water at the surface of the particle is quite rapid, resulting in an almost instantaneous formation of a semi-solid film through which moisture must diffuse from the interior, in order to evaporate at the surface. Heat is absorbed faster than it can be .used up by the surface evaporation of water,

with the result that the temperature within the interior of the particle rapidly increases. When the temperature exceeds the boiling point of water, steam pressure is generated within the particle which is compensated for in part by the expansion of the semi-solid, though extensible, surface layer until the point is reached if the expansion is carried far enough, where the film is ruptured and the pressure thus released. A microscopic examination of such particles will almost invariably disclose a blow hole. The degree to which this pufling of the individual particles takes place will depend upon the rate at which heat is absorbed by the particles. In this the controlling factor for a given solution is the temperature of the drying air current. The degree of pufiing is proportional to the influent air temperature.

Referring now more particularly to the drawings, the soap which is to be atomized and spray dried, is held-in solution in water in a supply reservoir 1 provided with heating coils for maintaining the temperature of the soap solution ranging between 160 and 220 F. A satisfactory temperature is about 190 F. The water content of this solution preferably ranges between 40% and 50% of the total and the solution is of such a consistency as to be' readily handled through pipe lines by a pump capable of handling viscous liquids.

By means of a pump 2 the soap-solution is circulated in a closed circuit through pipe 3, returning to the reservoir 1. Leading from this pipe 3, preferably at a point relatively near the spray equipment, is a feed line 4 leading to the spray equipment. The amount of soap solution diverted to this feed line may be controlled by valves 5 and 6, which, it is obvious, may be operated to give any desired volume of flow up to the capacity of the pump 2.

Incorporated with this soap feedline 1 is a superheater 7 of any preferred type, which provides means for raising the temperature of the soap solution fed to the spraying de vice to a degree beyond that possible under ordinary atmospheric pressure. This is due to the fact that the soap in this feed line is under the pressures built up by the pump working against the total resistance of the feed line 4 up to the point at which the discharge takes place at the atomizing device. The soap feed line 4 is also provided with connections for cleaning either with steam or water as shown by the pipes 8 and 9 and the three-way cock 1'0. Y

The spraymg or atom-zing device 11 (shown in more detail in Fig.3) consists of a spinning cup 12 carried upon a hollow r0- tating shaft 13 driven by a-steam turbine 14 or other suitable mechanism for providing a variable speed .of rotation. This hollow cup is rotated within a hollow cone or cylinder 15 whose inner surface in conjunction with the outer surface of the spinning cup 12 forms a plenum chamber 16 terminating in an annular orifice 17 surrounding the spinning cup. This plenum chamber 16 is supplied with air at relatively high pressure ranging from 15 to 25 inches of water, and preferably at a temperature ranging from 300 to 450 F., by the high pressure fan 18 drawing air through the heater 19 and communicating with the plenum chamber 16 by the duct 20. As hereinafter explained, it is not always necessary that the high pressure air should be heated.

The soap is supplied to the atomizing cup 12 by a pipe 21 leading from pipe 4, roperly supported within the hollow sha t 13, and terminating in a nozzle 22 so shaped as .to deliver the soap solution in a path approximately tangent to the inner surface of the spinning cup at the point of impact.

By virtue of the rotation'of the cup 12 and the contour of its inner face, the soap is caused to spread in an even layer over the surface which moves outwardly toward the rim of the cup, where the cup is of greatest diameter, ultimately leaving the free edge of the cup in a uniform spray which has a,

The atomizing action obtained by this spinning cup working in conjunction with the annular jet of high pressure air formed by the part 15 is susceptible'of producing a wide range of particle sizes which, however, under any given set of operating conditions, tend to be extremely uniform in size, providing the atomizing capacity ofthe ro'- tating cup is not excee ed.

For a cup of given diameter and length, the variables effecting the particle size are the angle or contour of the inner face of the cup, the speed of rotation of the cup and the pressure exerted by'the airagainst the sheet of spray as it leaves the edge of the cup. Another factor of importance in the operation of this spraying device is the position of vthe end 23 of the high pressure cone with respect to the delivery edge 24 of the spray cup. By moving the cone 15 forward so as to be more nearly in line with the edge of the spray cup, high pressure air of a given head may-be made to exert a greater effect in closing in .the cone of spray a second and larger truncated cone 25 which,

in conjunction with the passages leading thereto, forms a plenum chamber 26 for low pressure air supplied by the duct 27 comthe spraying device and supplying heat,

which may be supplemented by heat contained in the high pressure air, for carrying out the drying operation of the soap particles.

The volume of the high pressure air need be only about 15% to 35%, and is preferably from 20% to 30% of the total volume of the high and lowpressure air. The principal function of the high pressure air jet is to control the form ofthe spray cone and to furnish the kinetic force to project the spray particles through the horizontal chamber into the vertical tower. Consequently it is possible, if desired, to use unheated air for the high pressure jet, relying on the heat of the larger volume of low pressure air to perform the drying. The recommended temperature of the combined horizontal current of drying air is between 300 and 400 F., and referablyabout 325 to 350 F. It is there ore obvious that the temperature of the low pressure air of larger volume may be varied to secure the desired result according to the relative temperature and volume of the high pressure air.

The low pressure heated air may also be fed into the drying chamber 31 by duct 28 supplying air through branch duct 30 and port 35 at the rear of the chamber 31 tangential to the surface, this method of tangential entry being that commonly used in the ordinary cyclone separator. The use, or not, of such tangential air is optional.

The spray chamber 31 itself preferably consists of two principal sections, which, however, need'not be rigidly adhered to in the operation of the process. The section 32 farthest from the spraying nozzle is made up ,of curved surfaces, the elements of which are parallel to the axis of rotation forming a cross section of inverted pear shape as will be evident from the section shown in Fig. 2. The upper surface of this section is a true cylinder of approximately six foot radius while the depth of the lower section is approximately twelve feet below the axis of the cylindrical section just mentioned. The rear end wall 33' of the spray chamber is a flat circular plate approximately six feet in diameter while the remainder, 33, of the spray chamber nearest the spraying nozzle is of a truncated conoidal form of irregular section which can be most accurately described as the surface generated by a line moved about the axis of the spray cone at a uniform angular rate and remaining constantly in contact at one end with the circular back plate 33' and at the other end in contact with the edge of the pear-shaped section 32 at the front.

The spray chamber 31 opens upon a ver-,

tical tower 36 whose efiective height below the axis of the spray chamber is several times the height of the chamber itself. In practice a cylindrical tower approximately twenty feet in diameter and extending approximately forty feet below the axis of the spray chamberhas been found satisfactory.

The vertical tower 36 also preferably extends some distance above the spray chamber as shown. The upper part of the vertical tower above the spray chamber forms a passage for the current of heated air to a suitable flue or vent near the top, and the lower part of the vertical tower below the spray chamber forms a cooling zone into which the particles, separated by gravity from the current of heated air, fall. Since the capacity, or cross-sectional area, of the verticaltower is substantially larger than that of the spray chamber, it will be seen that the velocity of the current of heated air upon entering the vertical tower will be materially reduced, to a point below the conveying velocity for the denser particles, which are suitable for the finished product, thus permitting the latter to fall by gravity out of the heated air current and into the cooling zone below, while lightest and most expanded particles which are not desired in the finished product, will be carried on with the air current, although of reduced velocity, through the upper part of the tower to the vent.

Thereason for the inverted pear-shaped section of the spray chamber is to provide a means of carrying out of the spray chamber any particles of dried soap which may fall out of the air currents which, in a general way, are moving from the spray chamber into the tower. The sides of the pear-shaped section, as well as the lower half of the conoidal section 33 at the rear, are sufficiently steep to permit the dry particels to slide to the lower surface of the chamber from which they are swept out by a series of air jets 34 which are also supplied with air from the low pressure air duct 28. The heat in this air is also utilized in drying the product as it tends to diffuse through the spray of soap in its natural upward path to'the top of the tower.

The function of the tangential air previously referred to as entering the spra chamber by the duct 28, 30, through the mlet 35, if used, is to give a whirl to the entire air within the spray chamber and to sweep clean the inner surface of the latter.

After leaving the spray chamber and entering the tower 36 the soap particles are carried by gravity to the bottom of the tower 36, at which point they may be removed by an air lock 37 or other suitable device which deposits the product in a belt conveyor 38, by which the product may be fed to the i packaging machines.

, particles, which are undesirable in the finforce of gravity.

locities should be avoided.

ished product, passes out of the tower through a flue 39, which may be provided with an air filter 40. r

The air in the cooling zone of tower 36 below the spray chamber may be merely quiescent atmospheric air of ordinary room temperatures free from extrinsic currents. It is sometimes desirable, however, in order to maintain or modify the condition of the soap particles falling out of the current of heated air into the lower part of the tower 36, to introduce into the tower conditioned air whose temperature and humidity may be controlled to suit the requirements of the roduct. While this conditioned air may e introduced wherever desired in the path of the falling soap particles, it is preferably introduced as by duct 41, equipped with a blower '42, near the bottom of the tower, whence it rises in a' gentle draft toward the flue 39. An artificially cooled and humidified air will assist in the cooling of the soap product and in retaining in it, or even increasing if desired, the moisture content present when it passes out of the influence of the drying current of heated air.

It should be pointed out that in a tower of relatively large cross section, relatively large volumes of air can be allowed to remain quiescent, or can be moved gently either upwards or downwards in the lower part of the tower below the spray chamber without having any appreciable eflect on the falling velocity of the soap particles acting under the Of course conveying ve- Instead of venting the hot air at the flue 39 near the top of the tower, it is possible, if desired, to vent the hot air at a point in the tower below the spray drying chamber, thus carrying the drying operation farther along in the path of travel of the product before the product falls by gravity into the cooler part of the drying tower. Thus, it will be seen that the'moisture content of the soap particles when they leave the heat drying current of air, may be controlled by terminating or prolonging the influence of t'he heated air current, as well as by varying the temperature of the air current and/or the water content of the original soap solution.

The condition of the product made by a 66 spraying process of this nature may be varied all the way from small, -comparatively dense and approximatelyround particles to miniature rather heavy. walled spherical soap bubbles, depending 011 the regulation of the speed of the cup, its shape, the temperatures and volumes of high and low pressure air supplied to, the drying chamber and the physical condition of the soap solution itself.

An alternative construction for the horizontal spray chamber may take the form of a truncated cone-like drum, as illustrated in Fig'4, having a substantially horizontal axis,

with the spraying mechanism and air inflow at the smaller end. The flare or angle of the conoidal sides is such that the lower surface 43 of the cone enters the tower at an angle steeper than the angle of repose of the dried product upon the surface of the material of which the cone is built. This construction automatically carries into the tower both the particles which may drop out of the carrying effect of'the main air currents and also anymaterial which, due to improper operation of the, spraying mechanism, may have been plastered on the wall. The latter material pufls into a honeycombed mass and gradually slips off into the cooling tower 36 and is insufficient in bulk to materially affect the character of the principal product of the apparatus. In this construction the stepped jets or blowers 34 in the bottom of the pearshaped section of the horizontal spray chamber of the form shown in Fig. l, with their demand for air, are eliminated.

By spraying a very fluid hot soap solution into extremely hot air a maximum of putting or bubble formation is secured. If this soap is sprayed into cooler air the particles have less tendency to putt because the moisture has a chance to evaporate more without undue expansion of the interior moisture, leaving a comparatively round granule. If, however, the soap is allowed to cool before atomizing to the point where it tends to become stringy when dropped, the same tendency will persist to a degree in spraying from the rotating cup giving a rather round particle to which is appended a long stringy tail. Under the violent action of the air currents this tail may be broken up into relatively short pieces of a needle-like appearance. If this rather stringy soap is sprayed into rel- .atively cool air the product will consist of a pulled in the same manner that the globules have been pufled.

The process as above described is applicable to the handling of fluid soaps of varying chemical composition as regards both the fat stocks and the alkaline fillers, such as soda ash, sodium phosphate, silicate of soda, etc. A satisfactory Working formula is one giving a product containing: 60% pure soap, 25% soda ash, 15% sodium silicate.

Such a product is preferably made by spraying the fluid stock preheated to 180-200" F. and containing water and of solids. In handling such a formula in an apparatus of the dimensions heretofore specified as suitable for the purpose of practical operation it is recommended that the drying air be preheated to approximately 325-350 F., and that in spraying at the rate of 4000 pounds per hour of finished product, there be used upwards of 20,000 cubic feet of hot air per minute. Under these condi tions the finished products should have a gravity at least as high as .3 compared to Water.

The bulk weight of the product will usually be approximately 20 pounds per cubic foot, and certainly more than 15 pounds per cubic foot. The. product will contain from 15% to 20% of water, and the physical structure of the individual particles will consist of an outer shell only moderately extended or pulled, and not so unduly extended as to produce undesirable bulk, the interior hollow being cellular, that is, inthe form of a number of small voids, divided by thin films or walls, rather than in the form of a single void.

Because of the relatively high moisture content of our improved product it is readily soluble, and exhibits less tendency to form dust than previous heat-dried soap particles.

- The compactness of structure of the particles, and the conseqent relatively high bulk Weight of the particles enables a given amount of available soap to occupy a smaller volume than previous hot-spray dried soap products, with a resulting economy in packing and shipping;

The fat stocks from which the soap is made may be almost any mixture of tallow and vegetable oils as, for example, a mixture of tallow and cocoanut oil in the proportions of 75 to 25. Generally, it will be found desirable to use at least 25% of a high titre stock, such as tallow. Palm oil can be used in part as a substitute for tallow in the above formula.

No claims are herein presented for the novel appa? 15 above described, but the sub ect matter from the process and product, is claimed in a separate application, Serial No. 302,633, filed August 28, 1928, entitled Apparatus for the spray drying of soap. I

The novel product described herein constitutes the subject matter of our application the apparatus, as distinguished Serial No. 415,101, filed December 18, 1929, for patent on sprayed soap product.

We claim:

1. The art of drying soap which comprises atomizing a fluid soap solution, subjecting the atomized fluid particles to the drying action of heated air, separating the particles by gravity from the heated air at a predetermined stage in their drying process, and cooling the particles after separation by permitting them to fall through a zone of relatively cool air.

2. The art of drying soap which comprises atomizing a fluid soap solution, subjecting the atomized fluid particles to the drying action of a heated air current moving directionally therewith, separating the particles by gravity from the heated air at a predetermined stage in their drying process, and cooling the particles after separation by permitting them to fall through a zone of relatively cool air.

3. The art of drying soap which comprises atomizin g a fluid soap solution, subjecting the atomized fluid particles to the drying action of heated air, separating the partially dried particles by gravity from the heated air before they have been dried to a moisture content below 15%, and cooling the particles by permitting them to fall through a zone of relatively cool air.

4. The art of drying soap which comprises atomizing a fluid soap solution, subjecting the atomized fluid particles to the drying action of heated air, separating the partially dried particles by gravity from the heated air at that stage in the drying process at which they have a weight of approximately twenty pounds per cubic foot of bulk, and cooling the particles by permitting them to fall through a zone of relatively cool air.

5. The art of drying soap which comprises atomizing a fluid soap solution having an initial water content of not more than 50%, subjecting the atomized fluid particles to the drying action of heated air, separating the particles by gravity from the heated air at a predetermined stage in their drying process, and cooling the particles after separation by permitting them to fall through a zone of relatively cool air.

6. The art of drying soap which comprises atomizing a fluid soap solution having an initial water content of not more than 50%, subjecting the stream of atomized fluid particles to the drying action of a heated air current moving directionally therewith, separat- I ing the partially dried particles by gravity from the heated air current before they have been reduced to a moisture content below 15% or a weight below twenty pounds per cubic foot, and cooling the particles by permitting them to fall through a zone of relatively cool alr.

7. The art ofdrying soap which comprises atomizing a fluid soap solution, subjecting the atomized fluid particles to the drying action of a current of air heated to between 300 and 400 F., moving directionally therewith, separating the particles by gravity from the heated air at a predetermined stage in their drying process, and cooling the particles after ess, and cooling the particles after separation by permitting them to fall through a zone of relatively cool air.

9. The art of drying soap which comprises atomizing a fluid soapsolution having an initial water content of not more than 50%, subjecting the atomized fluid particles to the drying action of a current of air heated to between 300 and 400 F., moving direction ally therewith, separating the particles by gravity from the heated air at a predetermined stage in their drying process, and cooling the particles after separation by permitting them'to fall through a zone of relatively cool air.

10. The art of drying soap which comprises atomizing a fluid soap solution having an initial water content of not more than and an initial temperature of between160 and 220 F., subjecting the atomized fluid particles to the drying action of a current of air heated to between 300 and 400 F., moving directionally therewith, separating the particles by gravity from the heated air at.a predetermined stage in their drying process, and cooling the particles after separation by permitting them to fall through a zone of relatively cool air.

11. The art of drying soap which comprises atomizing a fluid soap solution, subjecting the.

atomized fluid particles to the drying effect of a heated air current, separating the particles by gravity from the heated air current at a predetermined stage in their drying process, and cooling the particles after separation by permitting themto fall through an upward current of relatively cool air.

12. The art of drying soap which comprises atomizing a fluid soap solution, subjecting the atomized fluid particles to the drying eflect of a heated air current, separating the particles by gravity from the heated air current at a predetermined stage in their drying process,

and cooling the particles after separation by permitting them to fall through a current of conditioned air.

I 13. The art of drying soap which comprises atomizing a fluid soap solution, subjecting the atomized fluid particles to the drying cf;- feet of a heated air current, separating the partially solidified particles by gravity from the heated air current at a predetermined stage in their drying process, and thereafter completing their solidification by permitting the particles to fall through a zone of relatively cool air.

14. The art of drying soap which comprises atomizing a fluid soap solution, discharging the atomlzed fluid particles horizontally into a concurrent stream of heated drying gas for drying said. particles and carrying them horizontally, separating the particles by gravity'from the current of heated air, and. 'maintaining an upward current of unheated air through which said separated particles fall.

15, The art of making a partially dried soap product of approximatel uniformly sized particles which comprises orming finely divided particles of various sizes from an initially fluid soap stock, subjecting the finely divided particles to the dryinglefi'ect of a current of heated air'by which t e particles are carried along,.transferring the coarser particles when only partiallydried from the current ofheated air into a zone of relatively cool air to eflfect theircooling and solidification, and conveying the finest particles awaywith the current of heated air.

16. Process of manufacture of soap, comprising atomizing a liquid soap solution, subjecting the atomized liquid particles to drying action of heated air, thusflreducing the water content of said particles by'evaporation, separating the said particles by gravity from the heated air at a predetermined stage of waterreduction, thereafter cooling the particles without appreciable further reduction of water content, by permitting them to fall through relatively cool air. I

17. Process of soap manufacture, characterized by atomizing liquid soap in particles into hot air, reducing the water. content and progressively thickening the soap of the particles by evaporation without sensibly lowering the temperature, then, at a predetermined stage of water-content reduction by evaporation, separating the particles from the hot air by gravity, thereafter allowing the particles tofall through relatively cool air, further solidifying the soap thereof by lowering temperature without appreciably decreasing the water content. a Signedby us at Boston, Massachusetts, this 24th day of August, 1928.

EARL P. STEVENSON. BEN B. FOGLER. 

